In leaded semiconductor chip packages, a chip is generally affixed to a leadframe using a permanent adhesive. In some cases, it is desirable to enhance the thermal performance of a package by improving the path for the departure of heat from the chip to an outside surface of the package. In many such cases, it is known to incorporate a heat spreader into the leadframe structure, for example, by welding, taping, or gluing the heat spreader to the chip-mount portion of the leadframe. In other cases, a heat spreader is riveted in place on the leadframe, and a chip is mounted directly to the heat spreader surface. In either case, due to its heat conduction properties, the heat spreader is typically made from metal, such as copper or copper alloy. In some instances, in order to increase its heat conduction, the heat spreader is large relative to the chip, extending in a plane parallel with the proximal ends of the leadfingers. This type of arrangement of chip, leadfingers, and heat spreader at least partially underlying the leadfingers, is used in many applications, but is not without its problems.
Electrical connections within a semiconductor chip package are commonly made by bonding wires from bond pads on the surface of the chip to the proximal ends of the leadfingers. The leadfingers typically extend from one end adjacent to a gap in the leadframe proximal to the chip, to a distal end at the exterior of the package where electrical connections may be made to the outside world. During a typical wirebonding process, a ball bond is formed on a bond pad of the chip using heat, pressure, and in many cases ultrasonic vibrations. The wire is then pulled to the proximal end of a leadfinger, and a stitch bond is formed there, also using some combination of heat and pressure, and often ultrasonic vibrations.
Wirebonding equipment generally includes a heat block, made of rigid material, for providing heat and supporting the leadframe during wirebonding. Pursuant to a wirebonding process, the heat block is heated to a predetermined temperature. A leadframe assembly including a leadframe, chip, and heat spreader, is placed in a cavity provided in the heat block and is typically secured in place by an associated clamp. Wirebonds are then made from the chip to the leadfingers and the assembly is thereafter removed from the heat block for further processing, such as encapsulation and ultimate separation. In many applications, supporting the proximal ends of the leadfingers during wirebonding is simply a matter of placing the leadframe assembly into a supporting cavity of a heat block.
The present invention is directed to overcoming, or at least reducing, problems present in the prior art, and contributes one or more heretofore unforeseen advantages, indicated herein, for providing improved heat blocks, and related methods for their use in the manufacture of improved semiconductor chip package assemblies.